1. Field of the Invention
The invention relates to friction engaging devices such as a clutch and a brake. More particularly, the invention relates to a lubricating structure for lubricating a friction member.
2. Description of the Related Art
Friction engaging devices in each of which a friction member is provided around the perimeter of a cylindrical rotating drum, and the rotating drum and a predetermined coupling member are engaged with/disengaged from each other via the friction member, for example, a multi-disk clutch, a multi-disk brake, a belt brake and a one-way clutch, are widely used in a power transmission device such as an automatic transmission for a vehicle. For example, Japanese Patent Laid-Open Publication No. 04-69412 discloses a power transmission device in which a through hole is formed in a rotating drum, and lubricating oil inside the rotating drum flows outside the rotating drum through the through hole by centrifugal force so as to lubricate a friction member.
In order to make a power transmission device as compact as possible, for example, a ring gear of a planetary gear set may be spline-coupled to the inner surface of the rotating drum, and may be positioned by a snap ring or the like while the ring gear contacts an inward flange which is integrally provided with the rotating drum. However, in the case where the ring gear is provided inside the rotating drum, even when a through hole is formed in the rotating drum, the lubricating oil cannot be supplied sufficiently to the friction member provided around the perimeter of the rotating drum. Also, a through hole may be formed in the ring gear. However, in this case, there is a possibility that the strength of the ring gear will be reduced.